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                电压                </h1>
                <p>时间限制：10s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：256MB</p>			</div>
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                                <h3>题目描述</h3><p><div>你知道Just Odd Inventions社吗？这个公司的业务是&ldquo;只不过是奇妙的发明(Just Odd Inventions)&rdquo;。这里简称为JOI社。</div>
<div>JOI社的某个实验室中有着复杂的电路。电路由n个节点和m根细长的电阻组成。节点被标号为1~N</div>
<div>每个节点有一个可设定的状态【高电压】或者【低电压】。每个电阻连接两个节点，只有一端是高电压，另一端是低电压的电阻才会有电流流过。两端都是高电压或者低电压的电阻不会有电流流过。</div>
<div>某天，JOI社为了维护电路，选择了一根电阻，为了能让【只有这根电阻上的电流停止流动，其他M-1根电阻中都有电流流过】，需要调节各节点的电压。为了满足这个条件，能选择的电阻共有多少根？</div>
<div>对了，JOI社这个奇妙的电路是用在什么样的发明上的呢？这是公司内的最高机密，除了社长以外谁都不知道哦~</div>
<div>现在给出电路的信息，请你输出电路维护时可以选择使其不流的电阻的个数。</div>
<p></p></p><hr/><h3>输入格式</h3><p><div>第一行两个空格分隔的正整数N和M，表示电路中有N个节点和M根电阻。</div>
<div>接下来M行，第i行有两个空格分隔的正整数Ai和Bi(1&lt;=Ai&lt;=N,1&lt;=Bi&lt;=N,Ai&ne;Bi)，表示第i个电阻连接节点Ai和节点Bi。</div>
<p></p></p><hr/><h3>输出格式</h3><p><div>输出一行一个整数，代表电路维护时可选择的使其不流的电阻个数。</div>
<p></p></p><hr/><h3>样例输入</h3><pre>4 4
1 2
2 3
3 2
4 3</pre><hr/><h3>样例输出</h3><pre>2</pre><hr/><h3>提示</h3><p><div>可以选择第一根电阻或第四根电阻。</div>
<div>&nbsp;<img src="../file/4238_0.jpg" width="364" height="174" alt="" /></div>
<div>2&lt;=N&lt;=10^5</div>
<div>1&lt;=M&lt;=2*10^5</div>
<div>不保证图是连通的，不保证没有重边</div>
<p></p></p><hr/><h3>题目来源</h3><p>JOI 2013~2014 春季training合宿 竞技3 By PoPoQQQ</p>
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